The invention relates to topical compositions for application to human skin and to their use in lightening human skin.
Many people are concerned with the degree of pigmentation of their skin. For example, people with age spots or freckles may wish such pigmented spots to be less pronounced. Others may wish to reduce the skin darkening caused by exposure to sunlight or to lighten their natural skin colour. To meet this need many attempts have been made to develop products that reduce the pigment production in the melanocytes. However, the substances thusfar identified tend to have undesirable side effects, e.g. skin irritation. Consequently such substances are not suitable for cosmetic use or they can only be applied at a concentration at which their skin lightening effect is less than desired. Using a combination of different skin lightening substances may be considered to reduce adverse side effects but there is a substantial risk that by using such a combination the skin lightening is reduced as well due to competition effects. Therefore there is a need for improvement in the effectiveness of cosmetic skin lightening products.
GB 2 287 405 discloses a skin-whitening cosmetic preparation that comprises in combination an extract of Glycyrrhyza glabra or a related plant species and an xcex1-hydroxy-, xcex2-hydroxy- or keto-acid or an amide, salt or ester thereof. The combination is said to act synergistically to inhibit tyrosinase thus inhibiting melanin formation.
WO 94/07462 discloses compositions inter alia to lighten the skin that comprise retinol or a derivative thereof and a dioic acid.
WO 94/09756 proposes the use of retinol or a derivative thereof together with a selected skin lightening agent for several purposes including lightening skin colour. The preferred skin lightening agent is hydroquinone but several others are mentioned as well, including liquorice extract.
U.S. Pat. No. 4,990,330 describes skin-whitening products that contain kojic acid in combination with another substance to be chosen from a range of materials including azelaic acid. The combination is reported to synergistically inhibit melanin synthesis.
JP 63284119 according to the Derwent abstract proposes a skin external agent with UV-preventing and whitening effects that contains isoferulic acid or a salt thereof and an organic acid or a salt thereof.
J06199646 according to the Derwent abstract describes a cosmetic to whiten skin that contains a plant extract, urea and a urea stabiliser. The extract can be chosen from a wide range of plants including glycyrrhizae radix (licorice root). The urea stabiliser can likewise be chosen from a broad group which group includes aliphatic dicarboxylic acids.
The above described products have thusfar not found wide acceptance and there continues to be a need for improvement in the area.
We have now found that enhanced reduction of melanin production can be obtained through the application of cosmetic compositions to the skin which comprise a specific isomer of conjugated linoleic acid or derivatives thereof.
According to a first aspect of the present invention there is provided a topical composition comprising:
(a) conjugated linoleic acid, and/or derivatives thereof comprising conjugated linoleic acid moieties, in which at least 1% by weight of the conjugated linoleic acid and/or moieties is present as the trans 10 cis 12 isomer; and
(b) a dermatologically acceptable vehicle.
Such compositions are particularly useful for topical application to human skin for enhancing the reduction of melanin production and thus lightening the skin on which it has been applied.
According to a second aspect, the present invention provides a cosmetic method for lightening human skin, the method comprising application to the skin of a topical composition as described above.
In a further aspect, the invention also provides the use of conjugated linoleic acid, and/or derivatives thereof comprising conjugated linoleic acid moieties, in a topical composition for lightening human skin, wherein at least 1% by weight of the conjugated linoleic acid and/or moieties is present as the trans 10 cis 12 isomer.
In a still further aspect of the invention, the reversal of the skin lightening action of the above described conjugated linoleic acid and/or derivatives is avoided through inclusion of an ultraviolet absorbing sunscreen in the compositions according to the first aspect of the present invention. By the term xe2x80x9csunscreenxe2x80x9d is meant any material whether organic or inorganic which can shield the skin from ultraviolet radiation within the range of 290 to 400 nm.
Trans 10, Cis 12 Isomer Containing Conjugated Linoleic Acid
Conjugated linoleic acid(hereinafter described as CLA) comprises a group of positional and geometric isomers of linoleic acid in which various configurations of cis and trans double bonds at positions (6, 8), (7, 9), (8, 10), (9, 11), (10, 12) or (11, 13) are possible. Thus twenty-four different isomers of the CLA exist.
The essential active of the compositions in accordance with the present invention is the trans 10 cis12 (hereinafter referred to as t10 c12) isomer. This particular isomer of the free acid has the structure (I) shown below: 
The invention also includes derivatives of the free acid which thus comprise conjugated linoleic acid moieties. Preferable derivatives include those derived from substitution of the carboxyl group of the acid, such as esters (eg retinyl esters, triglyceride esters, monoglyceride esters, diglyceride esters, phosphoesters), amides (eg ceramide derivatives), salts (eg alkali metal and alkali earth metal salts, ammonium salts); and/or those derived from substitution of the C18 carbon chain, such as alpha hydroxy and/or beta hydroxy derivatives.
In the case of triglyceride ester derivatives, all positional isomers of CLA substituents on the glycerol backbone are included. The triglycerides must contain at least one CLA moiety. For example, of the three esterifiable positions on the glycerol backbone, the 1 and 2 positions may be esterified with CLA and by another lipid at position 3 or as an alternative, the glycerol backbone could be esterified by CLA at the 1 and 3 positions with another lipid at position 2.
Wherever the term xe2x80x9cconjugated linoleic acidxe2x80x9d or xe2x80x9cCLAxe2x80x9d is used in this specification it is to be understood that the derivatives thereof comprising CLA moieties are also included.
xe2x80x9cCLA moietiesxe2x80x9d refers to the CLA fatty acyl portion(s) of a CLA derivative.
By xe2x80x9ct10 c12 isomer containing CLAxe2x80x9d is meant that at least 1% by weight of the total CLA and/or CLA moieties present in the composition is in the form of the trans 10, cis 12 isomer. Preferably, at least 20%, most preferably at least 50%, by weight of the total CLA and/or moieties present in the composition, is in the form of the t10 c12 isomer. In a particularly preferred embodiment at least 70% by weight of the total CLA and/or moieties is in the form of the t10 c12 isomer.
The CLA and/or derivatives thereof comprising CLA moieties according to the present invention may be prepared according to the method disclosed in WO 97/18320. A preferred method of preparation is disclosed in Example 1 below.
The active, t10 c12 isomer containing CLA, to be employed in accordance with the present invention is present in the topical composition in an effective amount. Normally the total amount of the active is present in an amount between 0.00001% and 50% by weight of the composition. More preferably the amount is from 0.01% to 10% and most preferably from 0.1% to 5% in order to maximise benefits at a minimum cost.
Dermatologically Acceptable Vehicle
The composition according to the invention also comprises a dermatologically/cosmetically acceptable vehicle to act as a dilutant, dispersant or carrier for the active, t10, c12 isomer enriched CLA. The vehicle may comprise materials commonly employed in skin care products such as water, liquid or solid emollients, silicone oils, emulsifiers, solvents, humectants, thickeners, powders, propellants and the like.
The vehicle will usually form from 5% to 99.9%, preferably from 25% to 80% by weight of the composition, and can, in the absence of other cosmetic adjuncts, form the balance of the composition.
Optional Skin Benefit Materials and Cosmetic Adjuncts
Besides the active, t10, c12 isomer containing CLA , other specific skin-benefit actives such as sunscreens, and/or other skin lightening agents, may also be included. When the sunscreen is an organic material, it will usually contain at least one chromophoric agent absorbing within the ultraviolet range somewhere from 290 to 400 nm. Chromophoric organic sunscreen agents may be divided into the following categories (with specific examples) including: p-Aminobenzoic acid, its salts and its derivatives (ethyl, isobutyl, glyceryl esters; p-dimethylaminobenzoic acid); Anthranilates (o-aminobenzoates; methyl, methyl, phenyl, benzyl, phenylethyl, linalyl, terpinyl, and cyclohexenyl esters); Salicylates (octyl, amyl, phenyl, benzyl, menthyl, glyceryl, and dipropyleneglycol esters); Cinnamic acid derivatives (menthyl and benzyl esters, a-phenyl cinnamonitrile; butyl cinnamoyl pyruvate); Dihydroxycinnamic acid derivatives (umbelliferone, methylumbelliferone, methylaceto-umbelliferone); Trihydroxycinnamic acid derivatives (esculetin, methylesculetin, daphnetin, and the glucosides, esculin and daphnin); Hydrocarbons (diphenylbutadiene, stilbene); Dibenzalacetone and benzalacetophenone; Naptholsulfonates (sodium salts of 2-naphthol-3,6-disulfonic and of 2-naphthol-6,8-disulfonic acids); Dihydroxy-napthoic acid and its salts; o- and p-Hydroxybiphenyldisulfonates; Coumarin derivatives (7-hydroxy, 7-methyl, 3-phenyl); Diazoles (2-acetyl-3-bromoindazole, phenyl benzoxazole, methyl naphthoxazole, various aryl benzothiazoles); Quinine salts (bisulfate, sulfate, chloride oleate and tannate); Quinoline derivatives (8-hydroxyquinoline salts, 2-phenylquinoline); Hydroxy- or methoxy-substituted benzophenones; Uric and vilouric acids; Tannic acid and its derivatives (e.g. hexaethylether); (Butyl carbityl) (6-propyl piperonyl) ether; Hydroquinone; Benzophenones (Oxybenzone, Sulisobenzone, Dioxybenzone, Benzoresorcinol, 2,2xe2x80x2, 4,4xe2x80x2-Tetrahydroxybenzophenone, 2,2xe2x80x2-Dihydroxy-4,4xe2x80x2-dimethoxybenzophenone, Octabenzone; 4-isopropyldibenzoylmethane, Butylmethoxydibenzoylmethane; Etocrylene; and 4-isopropyl-dibenzoylmethane).
Particularly useful are: 2-ethylhexyl p-methoxycinnamate,4,4xe2x80x2-t-butyl methoxydibenzoylmethane, 2-hydroxy-4-methoxybenzophenone, octyldimethyl p-aminobenzoic acid, digalloyltrioleate, 2,2-dihydroxy-4-methoxybenzophenone, ethyl-4-[bis(hydroxypropyl)]aminobenzoate, 2-ethylhexyl-2-cyano-3,3-diphenylacrylate, 2-ethylhexylsalicylate, glyceryl p-aminobenzoate, 3,3,5-trimethylcyclohexylsalicylate, methylanthranilate, p-dimethylaminobenzoic acid or aminobenzoate, 2-ethylhexyl p-dimethylaminobenzoate, 2-phenylbenzimidazole-5-sulfonic acid, 2-(p-dimethylaminophenyl)-5-sulfoniobenzoxazoic acid and mixtures thereof.
Suitable commercially available organic sunscreen agents are those identified under the following table.
Inorganic sunscreen actives may also be employed such as microfine titanium dioxide, zinc oxide, polyethylene, polyamides (e.g. nylon) and various other polymers. Amounts of the sunscreen agents (whether organic or inorganic) will generally range from 0.1 to 30%, preferably from 2 to 20%, optimally from 4 to 10% by weight.
The vehicle may also further include adjuncts such as perfumes, anti-oxidants, opacifiers, preservatives, colourants and buffers.
Product Preparation, Form, Use and Packaging
To prepare the topical composition according to the present invention the usual manner for preparing skin care products may be employed. The active components are generally incorporated in a dermatologically acceptable carrier in conventional manner. The active components can suitably first be dissolved or dispersed in a portion of the water or another solvent or liquid to be incorporated in the composition. The preferred compositions are oil-in-water or water-in-oil emulsions.
The composition may be in the form of conventional skin-care products such as a cream, gel or lotion or the like. The composition can also be in the form of a so-called xe2x80x9cwash-offxe2x80x9d product e.g. a bath or shower gel, possibly containing a delivery system for the actives to promote adherence to the skin during rinsing. Most preferably the product is a xe2x80x9cleave-onxe2x80x9d product; a product to be applied to the skin without a deliberate rinsing step soon after its application to the skin.
The composition may packaged in any suitable manner such as in a jar, a bottle, tube, roll-ball, or the like, in the conventional manner.
The product can be applied to the skin in the same way as conventional skin care products. e.g. it can be applied 1-3 times daily to the skin of e.g. the face and/or the hands and arms. In case of pigmented spots, the user may for example choose to apply the product only to the affected areas. The skin lightening will usually become visible after 2-3 months depending on the skin condition, the concentration of active components in the product and the amount of product and the frequency with which it is applied. The present product is particularly suitable for general skin lightening, especially if it also includes sunscreen agent in case the product is intended for daytime use.